Pink belly is usually one of the first signs they are going to shed.
Mine get a pink belly, then they get darker, then they get dull (go blue), then they clear up for a day or two and then they shed. ^__^
When you see his eyes starting to cloud up that's the time to really leave him alone until he sheds. They can't see like that and the oils from our skin can dry them out. Try to bump your humidity up if you can too, it will help him shed.
Also he might not eat right away if he's going to shed. I feed mine while they are shedding but I know a lot of people don't. Some ball pythons also won't eat when they are in the shed process.